docs: def data_folders(path):
          """ Generator which yields a list of valid data directories (corresponds to the content of one .tgz). """
          for item in os.listdir(path):
              dir_path = os.path.join(path, item)
              wav_folder = os.path.join(dir_path, 'wav')
  
              if os.path.isdir(dir_path) and os.path.isdir(wav_folder):
                  yield dir_path